Replicating the fancy touch sensor that uses anything

[Sprite_tm], a name many of you will recognize from these pages, has wasted no time in replicating the latest cool thing in a much simpler fashion. En Garde is a touch sensor that can detect up to 32 different points of contact on… whatever you use as the surface. He couldn’t sit idly by and let the Disney funded one from yesterday keep the spot light. As you can see in the video, it works pretty well. If he didn’t tell you that his can only detect up to 32 points as opposed to the 200 of the other, you probably wouldn’t even notice the difference. Of course, [Sprite_tm] also shares how you could easily beef his up to be even more precise. You can also download his source code an schematics from his site and give it a try yourself.

If you want a single axis, you’ll want a taper of surface area on each of two different interwoven sensors. e.g. █▉▊▋▌▍▏ or ◣ where each of black and white are the two different sensors. Then you measure the capacitive proximity to to each sensor and linearly extrapolate.

The other thing: The closest you can measure is approximately proportionate to the surface area of your sensor.

I recall someone, somewhere had turned their wall into a touch surface.

Was as simple as two piezo mics mounted on the wall. Tap the wall, measure the time until the tap is received at each mic, triangulate the position. This can only sense the initial tap.

Surface acoustic wave touchscreens work similarly, but actively generate ultrasonic waves/pulses in the surface, and detect how pressure from a finger reflects them; so they can sense prolonged touch. Just like sonar.

Both. I need transparency and multitouch. For experiments it would be enough to have a dualtouch.
Its really hard to find good sources with this conditions.

I’ve read this entry with appetite. I have currently hooked up some small transparent Resistive touchscreens on an Arduino. I use those cheap Nintendo DS screens. But these doint support multitouch; But I can learn from them.
I doint know how I can build a (ideality gap-less) surface in the dimension of 20x3000cm. I came to the point to look into custom made screens, but those are expensive, if even possible in extrem small quantities. Therefore I try to build it myself. As a beginner. Its hard! =(

Capacitive and resistive touchscreens both have transparent conductors on them. While it wouldn’t be impossible to make a giant touch surface with an ITO (indium tin oxide) matrix on it, I think only the most hardcore of us would attempt it on such a scale (like Jeri Ellworth)! That rules out those two technologies.

Multitouch also rules out both SAW, and infrared in the style of having a ring of emitters/detectors around the border.

That really leaves only one practical option with decent accuracy. Project infrared light on the back of a pane of glass, so that when finger(s) touch it, a camera can detect the point of contact. That’s the “detection of touch via frustrated total internal reflection” approach in the MIT paper Stefano linked.

Capacitive sensing as described in that paper has poor accuracy. Scanning laser rangefinders may be too difficult. Knock tracking is the approach I originally described (thanks for the link, Stefano).